Hurricanes: What's Next? is part of the University of Michigan's Teach-Out series. For more information, visit teachout.org.
The 2017 Atlantic Hurricane season has produced incredibly destructive storms, and has raised many questions. What drives a hurricane? How accurate are hurricane models? How do authorities prepare for hurricanes and, when destructive events like Hurricanes Harvey and Irma happen, how do we respond? Is this hurricane season a fluke, or should we start planning for more/similar storms? In this Teach-Out, we will explore the science of hurricanes, hurricane forecasting and monitoring, and with what confidence can we attribute these storms to a warming ocean.
A Teach-Out is:
-an event – it takes place over a fixed, short period of time
-an opportunity – it is open for free participation to everyone around the world
-a community – it will be joined by a large number of diverse individuals
-a conversation – an opportunity to give and take ideas and information from people
The University of Michigan Teach-Out Series provides just-in-time community learning events for participants around the world to come together in conversation with the U-M campus community, including faculty experts. The U-M Teach-Out Series is part of our deep commitment to engage the public in exploring and understanding the problems, events, and phenomena most important to society.
Teach-Outs are short learning experiences, each focused on a specific current issue. Attendees will come together over a few days not only to learn about a subject or event but also to gain skills. Teach-Outs are open to the world and are designed to bring together individuals with wide-ranging perspectives in respectful and deep conversation. These events are an opportunity for diverse learners and a multitude of experts to come together to ask questions of one another and explore new solutions to the pressing concerns of our global community. Come, join the conversation!
Find new opportunities at teach-out.org.

From the lesson

Hurricanes: What's Next?

The 2017 Atlantic Hurricane season has produced an alarming frequency of destructive storms, and with them, many questions. What drives a hurricane? How accurate are hurricane models? How do authorities prepare for hurricanes and, when destructive events like Hurricanes Harvey and Irma happen, how do we respond? Is this a fluke, or something we should start planning for?
In this Teach-Out, we will explore the science of hurricanes, hurricane forecasting and monitoring, and with what confidence can we attribute these storms to a warming ocean.

Meet the Instructors

Perry Samson

Arthur F Thurnau Professor, Professor of Climate and Space Sciences and Engineering, College of Engineering and Professor of Information, School of InformationCollege of Engineering; School of Information

Next, I'd like to discuss the science of hurricanes.

And we're gonna do that with Professor Ricky Rood, from Climate and

Space Sciences and Engineering at the University of Michigan.

Ricky is an expert in hurricane science and I've got some hard questions for you.

Ricky, first of all, 2017 what the heck?

Why are so

many hurricanes in this particular year is there something unusual?

>> Well the hurricanes vary in the Atlantic from year to year and

found some special conditions.

One of them is warm sea water, one of them is that there's not much variation in

the wind as you go up in the atmosphere cuz that keeps the hurricanes forming.

And then it's also helpful to have these disturbances coming off of Africa,

the Sahara Desert help organize them.

So we see years, sometimes with more hurricanes and sometimes with less.

One of the things that is extraordinary about

this year is that these three things have aligned.

And the Atlantic and the gulf of Mexico and

the Caribbean are extraordinarily warm.

>> Now often, when we have more hurricanes like this it's also,

there's an influence of El Nino, or La Nina.

How does that play a role this year?

>> I think currently we're at more of a neutral stage of El Nino and La Nina.

We had a strong El Nino and where there's an El Nino,

we tend to have fewer hurricanes in the Atlantic.

When there's a La Nina, the wind shear, that change of the wind

with altitude is usually weaker and we might have more.

But I believe with regard to the tropical situation we can not be said

right now to have an extraordinarily strong El Nino or La Nina.

>> The triggers for

many of these storms are easterly waves coming off the coast of Africa.

Is there then any increase or decrease change in these easterly waves this year?

>> To my knowledge there hasn't been what you might call a secular change.

We see more of those waves in some years than the other.

And we are seeing waves,

those easterly waves coming off of Africa, coming off the Sahara Desert.

Which occurs because of the very strong temperature gradient

in the Sahara sets off this very particular

type of wave that propagates to the east.

We don't often see waves propagating to the east, in general.

So they're a particularly interesting phenomenon.

But to my knowledge, we are seeing a year that has a number of them.

But we're not really seeing what you might call a climate trend

in these easterly waves.

>> Now when we track these storms it's not uncommon that the storms will

perturb the ocean.

They mix the water to a depth and leave a trail of cooler water behind.

But as I understand it, we've had IRMA and then there's JOSE.

And JOSE more or less followed IRMA.

And didn't really seem to decay.

Is there some change in the mixing that we're seeing in these storms?

>> I'm not sure that we would be seeing change particularly in

the mixing that's associated with the interaction of the air and the ocean.

But I think one of the things is extraordinary this year.

And one of the things that's definitely associated with climate change,

is that we are seeing the sea surface temperatures increase.

And more than that, we're seeing the ocean heat content.

So the amount of heat that's stored in the upper levels of the ocean

is increasing just one year after the other at this point.

That's where most of the heat of global warming goes is

to increase the ocean heat content.

So it's possible that the mixing is actually churning

up water that's not as cold historically.

Which would have an impact on the trailing hurricane.

>> The forecasting for Irma, although it changed

location sort of towards the end and went up the East Coast.

I'm sorry West Coast of Florida, for

the most part is pretty good forecasting best I could tell, the models vary.

I like you to speak about the variation and

various forecasting models for hurricanes.

>> So when we use models to provide guidance for

hurricanes, we rely on two classes of models.

One of them would be the global model.

And by global we mean that it attempts to, or doesn't attempt,

that its domain is the entire globe.

And then we also rely on regional models which allow us to

focus on only the hurricane region.

At the early phases what we really do rely on most are the global models.

And in this case, the global models were providing

reasonably good guidance well more than a week out.

This is a characteristic perhaps of these types of hurricanes

I think called Cape Verde hurricanes.

That are often associated with those African easterly waves

that they get picked up relatively early.

And the models can provide us a longer lead time on some of those,

then say on Harvey, which really formed right off the Texas coast.

So they're different characteristics there.

I think all in all the models did a extraordinary

job of providing guidance that there was

high likelihood of hurricane hitting Florida sometime in advance.

There will be some argument about the quality of the different models,

different global models.

That's already in the press floating around.

That's a longstanding issue about the differences between

the European Centers Model and the National Weather Services Model,

and the UK Met Office Model.

So that'll be an issue.

But hurricanes and their tracks are relatively difficult to

predict more than a few days in advance.

And what you saw as it got closer and closer to Florida that as we got more and

more data as the atmosphere stayed at a particular time and well defined.

The models started to alter that track of in terms

of the details of where it would hit on land.

These from a global perspective were not big alterations but for

a narrow state like Florida with a large hurricane like this.

These shifts of [INAUDIBLE] hundreds

of kilometers a small number of of hundreds of kilometers.

Can have very important consequences on the impacts.

And how you plan and how you prepare your evacuations.

>> Let's follow up on that issue of the modeling.

You mentioned the data that goes into these models is key to

the quality of the models.

What is the data that goes into these models now?

>> So the way weather forecasts are done, we use observations to

essentially take a snapshot of what the atmosphere and

the ocean and the land surface look like at a particular time.

And then what we do is we propagate the disturbances or

the weather that is present at that particular time.

We'll propagate that forward for the weather forecast.

So the data which goes into those models is and

the treatment of that data is probably the single

most important scientific decisions that

are made in terms of the ability to do a forecast.

Though there are many important decisions and all need to be made in concert.

So that data comes from many sources.

It comes from balloons and it comes from service stations.

It comes from airplanes.

And increasingly and by far the largest quantity of data comes

from a set of environment satellites.

And of particular importance in weather forecasting

are the data that come from of the polar orbiting satellites.

Which provide some information about the vertical structure of temperature.

And the vertical structure of moisture in the atmosphere.

So it's a combination of data from many sources

and there are literally millions, if not billions,

of observations incorporated into each weather forecast.

>> Can you describe the value of this new satellite GO 16?

I mean is the imagery from it is phenomenal.

So is that going to help us with forecasts in the future?

>> With regard to the science of using geostationary data like that.

It clearly provides a lot of information about sort of

the position of the hurricane, structure of the hurricane, the rain merge.

And it helps a whole lot on the short-term forecasting.

Those data will be difficult to incorperate into

the global forecast models so we think some progress.

The reason's it's difficult to incorporate in the global

forecast models, is that they staring down and

generally you see a very thick slab of the atmosphere.

So you do not see, alot of vertical structure, and

the vertical structure and how the temperature varies with high common and

how the moisture varies with high is crucial for the forecast.

>> [LAUGH] >> There's that train.

[LAUGH] >> Coming through.

Good.

I'll let the train pass for a second.

All right, the real elephant in the room here is that

the temperatures of the oceans are warming.

And you said a moment ago to greater depth, probably.

As we know, the amount of moisture the atmosphere can hold goes up exponentially

with temperature.

Given those two that, and understanding that the energy

of a hurricane comes from the condensation of water.

It's logical to expect, then, that the intensity or

duration of hurricanes might increase in the future.

What's your expectation?

>> So this is a problem that there's a lot of research on on what's happening.

One of the ways I think about this problem is it's

just stated the energy available through the warm water.

And for the warming ocean,

it's got to be having some sort of impact of these storms.

I don't see how you can add energy to a system and

not expect it to have some sort of impact.

The question is how is it changing these storms,

and are they different in some measurable way historically?

The people who knew the hard research on this.

Honestly, they end up with arguments about whether or not the frequency and

the intensity of the storms will change or if they have changed.

Most of the literature that I've read so far says that

it is reasonable to expect a larger number of these very strong storms.

But I think what is perhaps most interesting,

and what is perhaps ultimately going to be most important.

If you look at a storm like Irma and compare it say, to Andrew

the intensity of Andrew, the wind speed when it hit land was extraordinary.

But if you look at the size of these storms,

the size of these storms we've seen the last few years

is enormous compared to storms even two decades ago.

What is interesting to think about is that in terms of

energy is the amount of energy that is actually existing in these storms

though the peak wind may not be quite as large.

The amount of energy that is accumulated and

swirling around these storms is much, much larger.

And given the amount of energy in a spacial scale and

particularly when you get a slow moving storm.

The potential devastation especially perhaps from

flooding is the potential of that being greater is very high.

>> And of course the power of the wind goes up as the cube of the wind speed.

So, even small changes in wind speed and

area are gonna have a big impact on the total energy and power of a hurricane.

>> Absolutely and then the size and the wind interacting with the ocean

it pushes up the water that is associate with storm surges.

So you get an interesting phenomenon like we just had in Florida.

Where sometime after the storm reached its peak,

cities like Jacksonville Florida was getting extraordinary flooding.

With an extraordinary combination of rain and storm surge and

perhaps, increasing sea level.

>> Well Ricky thanks so much for your insights into these questions, and